In some types of communications networks, data stored in remote, data accumulation units are downloaded to a central computer or record keeping unit, periodically or on demand. For example, in electricity or other utility meter reading systems, to which the present invention is particularly advantageous but not necessarily limited, remote watthour meters are polled by a central computer which maintains customer electricity consumption records for billing. Typically there has been one centralized meter for each single-family home or for each apartment building occupied by a number of families, as well as for each single or multi-tenant commercial property, polled by a regional computer. It is preferable to monitor the electricity consumption of each user, rather than a community of users, to produce more equitable, individualized billing. However, it frequently is impractical to install separate meters in individual units, particularly in older apartment buildings, because there usually is no separate data communications line between each unit and a central site. Rewiring of the building is cost prohibitive. Accordingly, power lines provided to each unit and to which all meters are connected are used by the meters for transmitting electricity consumption data to a central computer. This is carried out by a transmitter in each meter which injects on the power lines a carrier signal modulated by data identifying the meter and reporting its consumption during a predetermined billing period.
However, because power lines are electrically noisy, it is difficult to establish a reliable communications link between the meters and the central computer using a reasonably small amount of signal power. Furthermore, the noise spectrum of the power lines changes with time of the day and season of the year depending on operation of electrical equipment connected, or located in proximity, to the power lines. For example, power line network characteristics have variations in attenuation as a function of frequency, with pronounced dips in transmission of some frequencies that vary among networks. Noise injected on the lines includes fixed frequency noise resulting, for example, from the switching of inductive loads. Other noise arises at harmonics of the frequency of the network, and there is gaussian background noise as well as fluctuating signals caused by appliances operating on the power lines.
Accordingly, one object of the invention is to provide a method of and system for establishing reliable communications between local and remote data reporting equipment.
Another object of the invention is to provide apparatus and methodology for establishing communications between central and remote units coupled to each other on an electrical power line wherein communications networking is carried out adaptively to route signals between the central and remote units along paths that tend not to be affected substantially by line noise.
Still another object is to provide reliable power line communications method and apparatus suitable for centralized meter reading.
Adaptive networks for selecting optimum signal paths on a power distribution network are known in the prior art. In Robinton U.S. Pat. No. 4,692,761, a power line based communication system for downloading data from remote units to a master unit on the electrical power line implements primary units at the nodes of the network that are capable both of transmitting and receiving messages and secondary units that are capable only of transmitting messages. Messages are transmitted between the remote units and the master unit in the form of data packets including power consumption data produced by a power meter associated with the initiating remote unit, addresses of source and destination nodes and data indicating whether the message is an up link message or a down link message. Additional data included in the packet indicate whether the message has arrived at its final destination or at an intermediate destination for relaying. Intermediate destination addresses are determined by information indicative of network conditions, such as the amount of noise, and present in messages transmitted by the originating or relaying node.
While generally satisfactory, this type of system is very complex, requires substantial data processing capabilities in nodes distributed throughout the network and is generally impractical for large systems, such as ones on the order of at least one thousand nodes, that may exist in large commercial or residential buildings or complexes. The number of units capable of operating as relays is limited and predetermined. The system furthermore is believed not to respond quickly to new adverse line noise conditions to develop new, more reliable, communication paths because the total path finding procedure must be implemented each time a communication is attempted.
Accordingly, another object of the invention is to provide an improved adaptive communications network that is less complex than adaptive communications networks known in the prior art.
Yet another object of the invention is to provide an adaptive communications network and method wherein the amount of data processing required therein is concentrated in a central control unit, not distributed throughout the network nodes.
Still a further object is to provide an adaptive communications network wherein new optimum communication paths as required are selected in a relatively short time period.
Another object is to provide an adaptive communications network wherein the number of nodes and the number of relays therein are unlimited.